64 lines
2.9 KiB
Markdown
64 lines
2.9 KiB
Markdown
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---
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obj: concept
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---
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# Adapter Pattern
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## **Description:**
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The Adapter Pattern is a structural design pattern that allows objects with incompatible interfaces to work together. It acts as a bridge between two incompatible interfaces, enabling them to collaborate without altering their source code. The Adapter Pattern is useful when you want to reuse existing classes or integrate third-party libraries that don't quite fit your desired interface.
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**How it's Used:**
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1. **Identify Interfaces**: Identify the two interfaces that need to work together but are incompatible.
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2. **Adapter Class**: Create an adapter class that implements the interface expected by the client code (the target interface) while containing an instance of the class with the incompatible interface (the adaptee).
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3. **Adapter Methods**: Within the adapter class, implement methods that map the methods of the target interface to the corresponding methods of the adaptee interface.
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4. **Client Code**: In the client code, use the adapter class to interact with the adaptee class as if it implements the target interface.
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## **Example:**
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Suppose you have a legacy class `OldSystem` with an interface that is incompatible with your modern system, but you need to integrate the legacy functionality. Here's how the Adapter Pattern can be applied:
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- **Incompatible Legacy Class (Adaptee)**: Define the `OldSystem` class with its existing interface.
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```java
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public class OldSystem {
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public void doOldStuff() {
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System.out.println("Doing old stuff in the legacy system.");
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}
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}
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```
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- **Target Interface**: Define the `NewSystem` interface that your modern system expects.
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```java
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public interface NewSystem {
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void doNewStuff();
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}
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```
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- **Adapter Class**: Create an adapter class `Adapter` that implements the `NewSystem` interface and contains an instance of the `OldSystem` class.
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```java
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public class Adapter implements NewSystem {
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private OldSystem oldSystem;
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public Adapter(OldSystem oldSystem) {
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this.oldSystem = oldSystem;
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}
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@Override
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public void doNewStuff() {
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// Delegate the new system's request to the old system's method
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oldSystem.doOldStuff();
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}
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}
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```
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- **Client Code**: In your modern system, use the `Adapter` class to work with the `OldSystem` as if it were a `NewSystem`.
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```java
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public class Client {
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public static void main(String[] args) {
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OldSystem legacySystem = new OldSystem();
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NewSystem adapter = new Adapter(legacySystem);
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// Use the adapter to perform new system operations
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adapter.doNewStuff();
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}
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}
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```
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By using the Adapter Pattern, you can integrate the legacy `OldSystem` class seamlessly into your modern system without changing the code of the legacy class. The adapter serves as a bridge, translating calls from the new system's interface to the old system's interface, allowing them to work together.
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